INCOME TAX- Differences between effective tax rates and the federal tax rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Differences between effective tax rates and the federal statutory rate applied to income before income taxes
Federal statutory income tax rate (as a percent)	35.00%	35.00%	35.00%
Federal statutory income tax	$ 17,661	$ 16,021	$ 12,871
Tax exempt interest	(4,799)	(4,676)	(4,425)
Effect of state income taxes	75	169	3,199
Non-deductible expenses	436	193	338
Tax exempt income on life insurance	(530)	(537)	(454)
Tax credits	(397)	(501)	(369)
Change in valuation allowance	(453)	(190)	(2,749)
Captive insurance premiums	(335)	(361)	(371)
Low income housing proportional amortization	419	363
Other	60	(248)	(261)
Total income tax expense	$ 12,137	$ 10,233	$ 7,779